Maxime Harnois

Engineering Sticky Superomniphobic Surfaces on Transparent and Flexible PDMS Substrate

Following the achievement of superhydrophobicity which prevents water adhesion on a surface, superomniphobicity extends this high repellency property to a wide range of liquids, including oils, solvents, and other low surface energy liquids. Recent theoretical approaches have yield to specific microstructures design criterion to achieve such surfaces, leading to superomniphobic structured silicon substrate. To transfer this technology on a flexible substrate, we use a polydimethylsiloxane (PDMS) molding process followed by surface chemical modification. It results in so-called sticky superomniphobic surfaces, exhibiting large apparent contact angles (>150°) along with large contact angle hysteresis (>10°). We then focus on the modified Cassie equation, considering the 1D aspect of wetting, to explain the behavior of droplets on these surfaces and compare experimental data to previous works to confirm the validity of this model.

Zipping Effect on Omniphobic Surfaces for Controlled Deposition of Minute Amounts of Fluid or Colloids

When a drop sits on a highly liquid-repellent surface (super-hydrophobic or super-omniphobic) made of periodic micrometer-sized posts, its contact-line can recede with very weak mechanical retention providing that the liquid stays on top of the microsized posts. Occurring in both sliding and evaporation processes, the achievement of low-contact-angle hysteresis (low retention) is required for discrete microfluidic applications involving liquid motion or self-cleaning; however, careful examination shows that during receding, a minute amount of liquid is left on top of the posts lying at the receding edge of the drop. For the first time, the heterogeneities of these deposits along the drop-receding contact-line are underlined. Both nonvolatile liquid and particle-laden water are used to quantitatively characterize what rules the volume distribution of deposited liquid. The experiments suggest that the dynamics of the liquid de-pinning cascade is likely to select the volume left on a specific post, involving the pinch-off and detachment of a liquid bridge. In an applied prospective, this phenomenon dismisses such surfaces for self-cleaning purposes, but offers an original way to deposit controlled amounts of liquid and (bio)-particles at well-targeted locations.

Contact angle hysteresis origins: Investigation on super-omniphobic surfaces

Contact angle hysteresis of liquid droplets is investigated on sticky and flexible super-omniphobic surfaces made up of PDMS–Si3N4 microstructures. Up to now, extensive studies have been focusing on the relation between hysteresis and surface properties such as roughness or defect density. However, little attention has been paid to the dependence of hysteresis with respect to the liquid surface tension. In this work, advancing and receding apparent contact angles are measured on surfaces displaying 4 different defect densities with 10 water–ethanol mixtures (surface energy ranging from 72 to 21.7 mN m−1). While advancing angles are found to be constant whatever the defect density and the liquid surface energy, receding angles exhibit more complex variations. Surprisingly, we noticed a saturation of this receding angle at low surface energy. In order to explain this phenomenon, we address the receding contact line distortion from the point of view of micro capillary bridges formation and breakage. The model is supported by fine SEM observation of the local deformation and offers a new perspective to explain the underlying mechanism of the saturation phenomenon.

Epoxy Based Ink as Versatile Material for Inkjet-Printed Devices.

Drop on Demand inkjet printing is an attractive method for device fabrication. However, the reliability of the key printing steps is still challenging. This explains why versatile functional inks are needed. Epoxy based ink described in this study could solve this critical issue because it can be printed with low drawbacks (satellites droplets, long-lived filaments, etc.). Moreover, a wide concentration range of solute allows the fabrication of films from thin to high aspect ratio. Optimizing experimental parameters (temperature, overlap) and ink composition (single or cosolvent) is useful to tune the film profile. As a result, many shapes can be obtained such as donuts or hemispherical caps for a droplet and smooth or wavy shape for a thin film. This study demonstrates that epoxy based versatile ink can be used in numerous fields of applications (organic electronics, optics, sensors, MEMS, etc.). To prove this assertion, organic field effect transistors and light emitting films have been fabricated.

An electron deficient dicyanovinylene-ladder-type pentaphenylene derivative for n-type organic field effect transistors

A bridged pentaphenylene derivative functionalized with dicyanovinylene units LPP([double bond, length as m-dash]C(CN)2)2 has been designed, synthesized and characterized. The optical and electrochemical properties have been carefully studied through a combined experimental and theoretical approach and compared with those of two pentaphenylene derivatives bearing methylenes (LPP) or carbonyl (LPP([double bond, length as m-dash]O)2) on the bridgeheads. LPP([double bond, length as m-dash]C(CN)2)2 which possesses a very low LUMO level, ca. −4.02 eV, has been successfully used as an active layer in n-channel OFETs using the epoxy based photoresist SU-8 as a gate insulator. LPP([double bond, length as m-dash]C(CN)2)2 based n-channel OFETs show low voltage functioning (low gate-source and drain-source voltages), high ratio between the on and the off currents (2 × 105), interesting subthreshold swing (S = 1) and excellent stability under electrical stress and in a nitrogen atmosphere. More importantly, we have also shown that LPP([double bond, length as m-dash]C(CN)2)2 based n-channel OFETs present an excellent environmental stability. This work is to the best of our knowledge the first report on bridged pentaphenylene-based semiconductors in n-type OFETs and highlights the potential of such type of material to provide air stable OFETs.

Characterization of the state of a droplet on a micro-textured silicon wafer using ultrasound

In this work, we propose acoustic characterization as a new method to probe wetting states on a superhydrophobic surface. The analysis of the multiple reflections of a longitudinal acoustic wave from solid-liquid and solid-vapor interfaces enables to distinguish between the two well known Cassie-Baxter and Wenzel wetting configurations. The phenomenon is investigated experimentally on silicon micro-pillars superhydrophobic surfaces and numerically using a finite difference time domain method. Numerical calculations of reflection coefficients show a good agreement with experimental measurements, and the method appears as a promising alternative to optical measurement methods.

Conformal Electronics Wrapped Around Daily Life Objects Using an Original Method: Water Transfer Printing

The water transfer printing method is used to transfer patterned films on random three-dimensional objects. This industrially viable technology has been demonstrated to intimately wrap metallic and polymeric films around different materials. This method avoids the use of rigid substrate during the transfer step. Patterns can be transferred to objects without folds even when holed, addressing a challenging issue in the field of conformal electronics. This technique allows high film bending properties to be reached. This promising method enables us to integrate large-area films onto daily life objects. A bent capacitive touchpad is fabricated showing the potential applications of this technology.

Electrowetting on functional fibers

We report on experiments of electrowetting on dielectric (EWOD) on functional fibers in air. Firstly, we investigate the evolution of drop contact angle θ with the applied voltage Vrms. θ(Vrms) relationship is compared to the theoretical Young–Dupre model and shows a good agreement at low voltage. However it appears that the saturation effect is different when compared to the EWOD response on a planar surface. We then study reversibility of the phenomenon to show that the drop recovers its initial shape when the voltage is switched off. Secondly, EWOD is used to modulate the maximal volume ΩM of a hanging drop. Results are compared to numerical simulations performed with Surface Evolver software. A good agreement is observed and it appears that ΩM increases linearly with Vrms. Finally, we present a proof of concept of a drop manipulation tool on fiber networks. This consists of an EWOD driven valve that is capable of regulating the drop traffic at a cross-junction between two fibers.

Direct Integration of Red-NIR Emissive Ceramic-like AnM6Xi8Xa6 Metal Cluster Salts in Organic Copolymers Using Supramolecular Interactions

Hybrid nanomaterials made of inorganic nanocomponents dispersed in an organic host raise an increasing interest as low-cost solution-processable functional materials. However, preventing phase segregation while allowing a high inorganic doping content remains a major challenge, and usual methods require a functionalization step prior integration. Herein, we report a new approach to design such nanocomposite in which ceramic-like metallic nanocluster compounds are embedded at 10 wt % in organic copolymers, without any functionalization. Dispersion homogeneity and stability are ensured by weak interactions occurring between the copolymer lateral chains and the nanocluster compound. Hybrids could be ink-jet printed and casted on a blue LED. This proof-of-concept device emits in the red-NIR area and generates singlet oxygen, O2 (1 Δg), of particular interest for lights, display, sensors or photodynamic based therapy applications.

Direct Electrical Detection of Biological Species

Suspended-Gate FETs, namely SGFET, with sub-micron gap, is shown to be able to detect biological species with very high sensitivity in a large range of concentration. Examples of detection of DNA (through the DelF508 mutation of the cystic fibrosis gene that is widely disseminating in Europe and North America, and one mutation of BRCA1 gene that is the main indication of the possibility for a woman to have breast cancer) and proteins (through the transferrin that is the only carrier of iron in blood) are presented. This very sensitive electrical detection without any labelling is shown to deliver directly readable signal.